1. Field of the Invention
This invention relates to a second-order IIR type digital filter and a reference signal canceling device and method using it.
2. Description of the Related Art
In FM stereo broadcasting, an FM detected signal includes a pilot signal at a single frequency of 19 KHz which is a reference for stereo demodulation. In order to cancel such a pilot signal, the circuit as shown in FIG. 4 has been proposed. Specifically, the pilot signal is extracted by a bandpass filter 20 which is an IIR (Infinite Impulse Response) filter and supplied to an attenuator 21, thereby canceling the pilot signal.
However, the above IIR filter provides changes in a central frequency and phase characteristic according to the accuracy in the coefficient of the filter. In order to remove the change, the number of bits of the coefficient must be increased. This gave raise to an increase in the circuit size and production cost.